1. Field of the Invention
The present invention relates to a laminate tape composed of a metal foil and a terpolymer resin coated on one or both surfaces of the metal foil, as well as to a laminate sheathed cable composed of a cable core and the laminate tape which is used as a masking layer to sheathe the core. More particularly, the invention relates to a laminate tape coated with a terpolymer resin of good adhesive properties not only for the metal foil but also for the polyethylene of a jacket layer, as well as to a laminate sheathed cable formed from said laminate tape.
2. Description of the Prior Art
Resins which are used as a coating layer for preparing laminate sheathed cables must have various characteristics, for example, they must have adhesive property which ensures they adhere not only to a metal foil but also to a jacketing compound, for example, polyethylene, they must be easily workable in the manufacture of a cable, for example, must have abrasion resistance in tape forming apparatus, and the like.
The reason for the necessity of the adhesiveness of the resin to the metal foil and to the polyethylene of the jacket layer is that any contraction of the polyethylene sheath is to be suppressed to improve not only the moisture resistance (that is, the prevention of moisture permeation from the outside) but also the mechanical strength (that is, the bending strength and the like) of the laminated or united sheath (or protective layer). This contraction is primarily because of inner strain generated in the plastic sheath, during the extrusion thereof, and resultant contraction due to the exposure of the polyethylene to the temperature cycle of the outside air.
As resins for forming such laminates, polyethylene has been used (see British Pat. No. 886,417). However, the conventional polyethylene resins are defective in that the adhesive power to an aluminum tape is weak.
In U.S. Pat. No. 3,233,036 a resin containing carboxyl groups is used to improve the adhesive strength to the aluminum tape. However, this prior art is also defective in that sufficient adhesive strength cannot be obtained due to the difference in polarity between the resin and the polyethylene of the protective jacket layer.
Japanese Patent Publication No. 23257/70 discloses a further improvement which is free from the two defects of low adhesive strength and mechanical properties, and provides a laminated tape of the so-called two-layer or multi-layer construction wherein an ethylene copolymer containing a carboxyl group which forms a chemical bond with a metal is coated on the surface which is to contact a metal foil (for example, an aluminum foil) and a resin which does not bind to the metal foil as effectively as the copolymer but which adheres to the jacket layer more firmly than the copolymer is applied to the surface which is not to be in contact with the metal foil.
When this kind of laminate tape is used, although the mechanical properties of the resulting cable are excellent, various faults are encountered in the preparation of laminate tapes, such as the manufacturing steps are complicated, the manufacturing cost is high and the cost of the resulting cables is high. This is because the thus prepared laminate tapes are composed of two layers or multiple layers.